[action] [PR:4787] [tempershow]: Avoid heavy SFP/xcvr import for port-name mapping

[mssonicbld]

What I did

Fixed a ~40% performance regression in show platform temperature (which invokes the tempershow utility). Fixes sonic-net/sonic-buildimage#28529.

tempershow maps each logical port name (e.g. Ethernet0) to the legacy xSFP module <N> Temp sensor label. It previously built this mapping by calling platform_sfputil_helper.load_platform_sfputil(), which imports the entire sonic_platform_base -> sonic_xcvr transceiver-API stack (CMIS/CDB/VDM/yaml/netaddr) plus utilities_common.cli. That import chain dominates the command's runtime even though the actual STATE_DB temperature read only takes a few milliseconds.

How I did it

• Build the {logical_port_name: front-panel index} map directly from the platform port configuration via portconfig.get_port_config, reading the same index field that SfpUtilHelper.read_porttab_mappings uses. This pulls in only swsscommon/sonic_py_common, which tempershow already imports.
• Dropped the utilities_common.platform_sfputil_helper dependency (and the heavy sonic_platform_base/sonic_xcvr import chain it triggers) from tempershow.
• Preserved single-ASIC and multi-ASIC namespace handling; if the port config is unavailable, the display name falls back to the logical port name, exactly as before.
• The xSFP module <N> Temp labels are byte-for-byte unchanged — only the heavy import is removed.
• Added tests/tempershow_test.py covering the new mapping (single/multi-ASIC, missing/failing port config, invalid index) and the display-name fallback.

How to verify it

1. Run the unit tests:

   pytest tests/tempershow_test.py -v
   

2. On a switch, confirm that the output of show platform temperature (including every xSFP module <N> Temp row) is unchanged before and after this change.
3. Confirm the heavy import chain is gone:

   python3 -X importtime /usr/local/bin/tempershow 2>&1 | grep -E 'sonic_platform_base|sonic_xcvr|portconfig'
   

   Before: the sonic_platform_base/sonic_xcvr chain is imported (~40 ms cumulative). After: only portconfig (~0.5 ms) is imported.

Hardware verification on a 202605 image — Mellanox-SN2700 (single-ASIC, SONiC.20260510.10, internal-202605 build, Python 3.13). The DUT-tested commit is byte-for-byte identical to this PR's scripts/tempershow and tests/tempershow_test.py.

Metric (7 runs each)	Baseline (heavy import)	Fixed (this PR)
End-to-end tempershow real time — median	0.328 s	0.233 s (~29% faster)
End-to-end tempershow real time — min / max	0.297 s / 0.371 s	0.224 s / 0.255 s
Isolated port-name mapping path	~0.283 s (platform_sfputil_helper)	~0.150 s (portconfig.get_port_config)
Heavy sonic_platform_base/sonic_xcvr chain at module load	~41.7 ms	eliminated (only portconfig, ~0.57 ms)

Functional correctness: output is 43 lines before and after, and all 32 xSFP module <N> Temp sensor labels (and their order) are byte-for-byte identical to the previous implementation.

Previous command output (if the output of a command-line utility has changed)

No change to command output. The show platform temperature / tempershow table (including the xSFP module <N> Temp labels) is identical before and after this change; only the runtime/import cost is reduced.

New command output (if the output of a command-line utility has changed)

N/A — output unchanged (see above).

Signed-off-by: Sonic Build Admin sonicbld@microsoft.com

[mssonicbld]

Original PR: sonic-net/sonic-utilities#4787

[mssonicbld]

/azp run

[mssonicbld]

/azp run